Detailing new evidence of Cold-War dangers, a report said yesterday that Moscow's nuclear-powered submarines had collided with foreign subs at least eight times over the decades and, separately, suffered at least four partial meltdowns of nuclear reactors.

The report also said that one reactor on a Soviet sub exploded in 1985 while being serviced at a shipyard, killing 10 people and releasing clouds of radioactive material that irradiated workers and caused at least one case of severe radiation sickness.

The four partial meltdowns of reactors occurred at sea. The crippled subs were able to return to port, although in two instances many seamen died of radiation poisoning, the report said.

Seven of the eight undersea collisions were apparently with U.S. submarines; the most recent one occurred a year ago in the Barents Sea, the report said. The eighth was with a British sub.

The report, by the environmental group Greenpeace, was based on a four-month trip the group took last year to Moscow and the Russian Far North and Far East, during which it conducted dozens of interviews with Russian and former Soviet officials, including a number of navy officers.

Since the collapse of the Soviet Union, the Russian military has described a number of accidents involving nuclear submarines. The report quoted navy officials as saying that submarine failures were decreasing but that the danger of collision persisted. It added that the Russian officers wanted to start East-West talks aimed at reducing such risks. Private experts say rival submariners often engage in games of underwater cat-and-mouse, a charge submariners deny. Some close tracking apparently done as practice.

While some of the collisions and meltdowns had been disclosed before, partly in the Russian press, the new report is by far the most detailed and complete listing of such problems to date. Greenpeace in recent years has gained a reputation for its thorough research on undersea matters.

"I take this very seriously," said Dr. Murray Feshbach, co-author of the book "Ecocide in the U.S.S.R." and a research professor at Georgetown University in Washington. "We're learning much more, and it's much worse than we ever knew before. It's a very dangerous situation, for them, and for us. It's one horror after another."

The report's author, Joshua Handler, said that the risk of submarine disasters could be rising because of "the bad times the Russian navy faces."

A Pentagon spokesman said the U.S. Navy has suffered no reactor meltdowns on submarines, but declined to discuss collisions. The United States has long maintained tight secrecy over the movements of its nuclear submarines.

Last year, after a U.S. nuclear submarine collided with a Russian sub in Arctic waters, Pentagon officials said they were not surprised and suggested there would be no policy change.